Taenia solium- Classification, Habitat, Structure, Body wall

Taenia solium is a parasitic tapeworm that belongs to the phylum Platyhelminthes, class Cestoda, order Cyclophyllidea, family Taeniidae and genus Taenia . The scientific name Taenia solium means "ribbon throne" in Latin, referring to its flattened body and ring of hooks on its head.

Taenia solium has two hosts in its life cycle: humans and pigs. Humans are the definitive or primary hosts, where the adult tapeworm lives in the small intestine and produces eggs or proglottids (segments) that are passed in the feces . Pigs are the intermediate or secondary hosts, where the eggs or proglottids hatch into larvae called cysticerci that invade the muscles and other tissues . Humans can also become intermediate hosts if they ingest eggs or proglottids from contaminated food or water, leading to a serious condition called cysticercosis .

Taenia solium is found worldwide, but it is more common in regions where pork is eaten raw or undercooked and where sanitation and hygiene are poor . Taenia solium can cause mild or no symptoms in humans as definitive hosts, but it can cause abdominal pain, nausea, diarrhea, weight loss and malnutrition in some cases . Cysticercosis can cause seizures, headaches, vision problems, meningitis and even death in humans as intermediate hosts .

Taenia solium can be treated with anthelmintic drugs such as praziquantel or niclosamide that kill the adult tapeworms in the intestine . Cysticercosis can be treated with antiparasitic drugs such as albendazole or praziquantel, along with anti-inflammatory drugs and anticonvulsants to reduce inflammation and prevent seizures . Prevention of Taenia solium infection involves cooking pork thoroughly, washing hands and food properly, avoiding contact with pig feces and treating infected people and pigs .

Taenia solium, also known as pork tapeworm, is found worldwide. Thus, its distribution is cosmopolitan. It is especially reported from the developing countries where pigs are raised in poor sanitary conditions and where pork is eaten, either raw or improperly cooked . In the Western Hemisphere, it is mostly found in South and Central America.

Its life cycle is completed in two hosts, i.e., digenetic; man being the primary host and pig as secondary host. Other animals like goats, cattle, monkeys, and horses also serve as intermediate hosts. In the definitive host, the adult tapeworm can be found in the small intestine (upper jejunum). The parasite remains attached to the intestinal mucosa with the help of hooks or rostellum.

It absorbs the host’s digestive food through its body wall. It does not have a mouth or digestive system of its own. It also lacks a circulatory and respiratory system. It relies on diffusion for gas exchange and nutrient transport.

Infection with T. solium tapeworms can result in human cysticercosis, which can be a very serious disease that can cause seizures and muscle or eye damage. More on: cysticercosis

Taenia solium, also known as pork tapeworm, is a parasitic flatworm that belongs to the class Cestoda. It has a complex life cycle that involves two hosts: humans and pigs. The adult tapeworm lives in the small intestine of humans, while the larval stage (cysticercus) infects the muscles and other tissues of pigs. Humans can also become infected with cysticerci by ingesting eggs from contaminated food or water.

The structure of Taenia solium can be described by three main parts: the scolex, the neck, and the strobila.

The scolex is the anterior end of the worm that attaches to the intestinal wall of the human host. It is knob-like, about 1 mm in diameter, and has four muscular suckers and a retractable rostellum with two rows of hooks. The suckers and hooks help the worm to anchor itself and resist being dislodged by peristalsis or digestion. The scolex also contains sensory receptors and nerve ganglia that control the movement and coordination of the worm.
The neck is a short, narrow, and unsegmented region behind the scolex. It is the site of growth and segmentation of the worm. New segments, called proglottids, are produced by transverse fission or budding from the neck region. The neck has a high regenerative capacity; if the scolex and neck are not removed by treatment, the worm can regenerate from this part.
The strobila is the long, ribbon-like body of the worm that consists of many proglottids arranged in a linear series. The strobila can reach up to 7 meters in length and contain up to 1000 proglottids. Each proglottid is a self-contained unit that has a complete set of male and female reproductive organs, as well as a part of the excretory and nervous system. The proglottids are classified into three types according to their maturity: immature, mature, and gravid. Immature proglottids are near the neck region and lack reproductive organs; mature proglottids are in the middle part of the strobila and have functional reproductive organs; gravid proglottids are at the posterior end of the strobila and contain a branched uterus filled with fertilized eggs. Gravid proglottids detach from the strobila and are passed out with the feces of the human host.

The body wall of Taenia solium consists of an outer tegument and an inner basement membrane. The tegument is a thick, waxy, and enzyme-resistant layer that covers the entire surface of the worm. It is composed of protein impregnated with calcium carbonate and has numerous fine pores and microvilli that help in absorption of nutrients from the host`s intestine. The tegument also protects the worm from immune responses and digestive enzymes of the host. The basement membrane includes both the musculature and the parenchyma. The musculature consists of circular and longitudinal muscle fibers that enable movement and contraction of the worm. The parenchyma is a loose network of cells and fluid-filled spaces that fill up the space between the organs and provide support to them. The parenchyma also contains calcareous bodies that are secreted by special cells and help to neutralize the acidity of the host`s digestive juice.

Taenia solium is usually opaque white, but creamish, yellowish, or greyish coloration is also common.
Its body is long (1-5 meters), dorsoventrally flattened, narrow, ribbon-like.
The two flat surfaces represent the dorsal and ventral surfaces, respectively.
The internal view reveals that the surface closer to the testes is dorsal, and nearer to the female reproductive organs is the ventral surface.
Its body narrows anteriorly and gradually broadens posteriorly.
The eggs of Taenia solium are spherical, brown in color (bile stained), and measure 30-40 µm in diameter . They are surrounded by embryophore which is brown, thick-walled, and radially striated.

The elongated body of Taenia solium is divided into many segments or parts with about 850, called proglottids. Segmentation of tapeworms is called pseudometamerism. The function of these segments is reproduction and nutrient exchange. Every segment of the tapeworm behaves independently. Hence, this type of segmentation is not considered as true metamerism as in Annelids.

The tapeworm body is divisible into three distinct parts: anterior scolex or head, a short-unsegmented neck, and a segmented strobila. The proglottids are budded off from the neck region and pushed back due to more proglottids in front. Anterior proglottids are youngest in strobila, and posterior ones are oldest. The proglottids bear genital papilla and pore, alternating once to the right and then to the left.

The proglottids are differentiated into three kinds according to the degree of development:

Immature proglottids: These are proglottids just behind the neck. These include nearly 200 anterior proglottids. They are the youngest, sexually immature, and devoid of reproductive organs. They are short, broader than long, and rectangular in outline.
Mature proglottids: They form the middle part of the strobila. They are about 450 in number. These are large and squarish in outline. The anterior 100 to 150 proglottids contain male reproductive organs only. The posterior 250 proglottids develop both male and female reproductive organs. Thus, mature proglottids are hermaphrodite.
Gravid proglottids: These are the oldest and towards the posterior end of the body. They include 150 to 350 proglottids. They are longer than broad in outline. They have no reproductive organs. They contain only branched uterus packed with fertilized eggs.

Small groups of gravid proglottids are regularly cut off from the posterior end of strobila and pass out with the host’s feces, called apolysis. Apolysis serves to transfer the developing embryos to the exterior, where the secondary hosts can ingest them. It also keeps the body’s size, which may otherwise attain enormous length due to the continued proliferation of new proglottids from the neck region.

The scolex is the anterior end of the body that serves as the organ of attachment to the intestinal mucosa of the human host. It is knob-like, biradially symmetrical, and about 0.6 to 1 mm wide . It has four cup-like muscular suckers that have radial muscles and help in adhesion. At its tip, there is a prominent rounded cone called the rostellum, which is armed with 22 to 32 curved and chitinous hooks arranged in two circles . The inner circle has larger hooks and the outer circle has smaller hooks. The hooks are conical and have a base, a handle, and a blade. The rostellum can be retracted or protruded and helps in piercing the intestinal wall of the host. The scolex of Taenia solium can be distinguished from that of Taenia saginata (the beef tapeworm) by the presence of hooks, as Taenia saginata has a scolex with four suckers but no rostellum or hooks . The scolex is connected to the neck region by a narrow isthmus.

The scolex is derived from the oncosphere, which is the larval stage that hatches from the egg after ingestion by the intermediate host (usually a pig). The oncosphere has six hooks and invades the intestinal wall, enters the bloodstream, and migrates to various tissues where it develops into a cysticercus. The cysticercus is a fluid-filled bladder with an inverted scolex inside. When a human eats undercooked pork containing cysticerci, the scolex evaginates and attaches to the small intestine, where it grows into an adult tapeworm .

The scolex is important for the survival and transmission of Taenia solium, as it enables the parasite to anchor itself to the host`s intestine and resist peristalsis and digestion. It also allows the parasite to infect new hosts by producing eggs that are shed in the feces of the definitive host (human) and ingested by intermediate hosts (pigs or other animals). The scolex can also cause serious complications if humans accidentally ingest eggs and develop cysticercosis, which is a disease caused by cysticerci in various organs, especially the brain (neurocysticercosis). Neurocysticercosis can cause seizures, headaches, hydrocephalus, and other neurological disorders .

The neck is a short and narrow region that connects the scolex and the strobila.
It is unsegmented and has no reproductive organs.
It is the region of growth and proliferation of new proglottids by transverse fission or asexual budding.
It is also called the budding zone, growth zone, area of proliferation, or segmentation area.
The neck is constantly growing and producing new proglottids that are pushed back by the older ones.
The neck is composed of the same body wall as the rest of the body, i.e., an outer tegument, an inner basement membrane with musculature, and a mesenchyme or parenchyma with calcareous bodies.

The strobila is the main part of the body that consists of many segments or proglottids arranged in a linear series.
The strobila measures about 3 meters in length and has about 800 to 1,000 proglottids.
The proglottids are budded off from the neck region and pushed back due to more proglottids in front.
The proglottids are differentiated into three kinds according to the degree of development: immature, mature, and gravid proglottids.
The immature proglottids are the youngest and sexually immature, and they are short and rectangular in shape.
The mature proglottids are hermaphrodite and have both male and female reproductive organs. They are large and squarish in shape.
The gravid proglottids are the oldest and contain only a branched uterus packed with fertilized eggs. They are longer than broad in shape.
The proglottids bear genital papilla and pore, alternating once to the right and then to the left.
The strobila serves to produce and release eggs that can infect the secondary hosts.

These are proglottids just behind the neck region.
These include nearly 200 anterior proglottids.
They are the youngest, sexually immature, and devoid of reproductive organs .
They are short, broader than long, and rectangular in outline.
They have no genital papilla or pore.

Mature proglottids are the middle part of the strobila, where both male and female reproductive organs are fully developed and functional.
They are about 450 in number and measure about 10 mm in length and 6 mm in width. They are squarish or slightly longer than broad in outline.
They have a single set of male and female reproductive organs in each proglottid. The male organs consist of testes, vasa efferentia, vas deferens, cirrus pouch, and cirrus. The female organs consist of ovary, oviduct, ootype, uterus, vagina, vitelline gland, vitelline duct, and genital pore.
The testes are numerous (100 to 150), small, oval or spherical bodies scattered in the medullary parenchyma. They produce sperms that are carried by the vasa efferentia to the vas deferens.
The vas deferens is a long, coiled tube that runs posteriorly and opens into the cirrus pouch. The cirrus pouch is a muscular sac that contains the cirrus, a protrusible copulatory organ armed with spines. The cirrus can be everted through the genital pore for mating with another proglottid.
The ovary is a bilobed structure located near the posterior margin of the proglottid. It produces ova that are carried by the oviduct to the ootype, a small chamber where fertilization takes place.
The ootype is connected to the uterus, a thin-walled sac that expands as it fills with fertilized eggs. The uterus has several lateral branches that radiate from the central stem. The uterus occupies most of the proglottid in gravid condition.
The vagina is a short tube that opens into the genital pore along with the cirrus. It receives sperms from another proglottid during copulation. It also has a sphincter muscle that prevents the entry of self-fertilization.
The vitelline gland is a large, compact mass of cells that produce yolk or vitelline cells. It is situated near the anterior margin of the proglottid. It gives rise to the vitelline duct that joins the oviduct near the ootype. The vitelline cells provide nourishment to the developing embryos in the uterus.
The genital pore is a common opening for both male and female organs. It is situated on the lateral margin of the proglottid, alternating from right to left in successive segments. It appears as a small elevation called the genital papilla.

These are the oldest and towards the posterior end of the body .
They include 150 to 350 proglottids.
They are longer than broad in outline .
They measure about 12 mm in length x 5-7 mm wide.
They have no reproductive organs .
They contain only branched uterus packed with fertilized eggs .
The uterus has a central stem with 7-13 main lateral branches on each side .
The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces .
T. solium may produce 50,000 eggs per proglottid .
The eggs are immediately infectious and do not require a developmental period outside the host.

Apolysis in Taenia solium

Apolysis is the process of detachment of the gravid proglottids (tapeworm segments containing fertilized eggs) from the posterior end of the strobila (the main body of the tapeworm) . Apolysis serves to transfer the developing embryos to the exterior, where the secondary hosts (such as pigs or humans) can ingest them . Apolysis also helps to maintain the size of the body, which may otherwise grow too long due to the continuous proliferation of new proglottids from the neck region .

In T. solium, like other tapeworms, the gravid proglottids are regularly cut off either singly or in groups of two to five proglottids . These detached proglottids are passed out from the body of the host during defecation along with the feces . The proglottids are motile and can crawl out of the anus or move within the feces . The proglottids contain about 50,000 eggs each, which are released when the proglottids disintegrate or are ruptured by mechanical or chemical agents .

The eggs are spherical, yellowish-brown, and have a thick radially striated shell . The eggs contain an oncosphere (a larval stage with six hooks) that is infective to the intermediate hosts . The eggs can survive for several months in moist soil or water . If ingested by a suitable intermediate host, such as a pig or a human, the eggs hatch in the small intestine and release the oncospheres . The oncospheres penetrate the intestinal wall and enter the bloodstream, where they are carried to various organs and tissues, such as muscles, brain, eyes, liver, and lungs . There they develop into cysticerci (bladder-like larvae with an inverted scolex) that cause cysticercosis .

Body wall of Taenia solium

The tapeworm lacks a cellular or ciliated epidermis. The body wall of Taenia consists of an outer tegument and inner basement membrane. The basement membrane includes both the musculature and the packing material called parenchyma.

Teguments in Taenia solium

Teguments are the outermost layer of the body wall of Taenia solium. They are thick, waxy, and resistant to digestive enzymes and immune attacks from the host. They are derived from tegumentary secretory cells that produce a proteinaceous substance impregnated with calcium carbonate. The teguments are perforated by numerous fine canals that allow the absorption of nutrients and excretion of waste products.

The teguments consist of three layers: the outermost comidial layer, the middle homogenous layer, and the innermost basement membrane. The comidial layer is composed of hair-like or finger-like projections called microtriches that increase the surface area for absorption and adhesion. The homogenous layer is a thick and smooth layer that contains mitochondria and lysosomes. The basement membrane is a thin layer that connects the tegument to the underlying musculature.

The teguments play an important role in the survival and adaptation of Taenia solium in the host`s intestine. They protect the parasite from mechanical damage, chemical digestion, and immune responses. They also help in the uptake of nutrients from the host`s digested food and the elimination of metabolic wastes. The teguments may also secrete substances that modulate the host`s immune system or interfere with its intestinal functions.

Integumentary musculature in Taenia solium

The integumentary musculature is the layer of muscle fibers that lies just below the basement membrane of the body wall. It consists of an outer circular and inner longitudinal layer of fibers that run along the length of the body. The circular fibers help to maintain the shape and rigidity of the body, while the longitudinal fibers help to contract and relax the body segments. The integumentary musculature also helps to move the scolex and the proglottids during attachment and detachment.

The integumentary musculature is connected to the mesenchymal musculature, which consists of longitudinal, transverse, circular, and vertical or dorsoventral muscle fibers that are embedded in the parenchyma. The mesenchymal musculature helps to adjust the shape and size of the internal organs and also assists in the expulsion of eggs from the gravid proglottids. The mesenchymal musculature is more developed in the scolex and the neck region than in the rest of the body.

The integumentary and mesenchymal musculature work together to provide movement and support to the body of Taenia solium. They also help to regulate the pressure and flow of fluids within the body cavity. The musculature is innervated by nerve fibers that originate from the nerve ring in the scolex and run along the longitudinal nerve cords on either side of the body.

Mesenchyme or parenchyma

The mesenchyme or parenchyma is the innermost layer of the body wall of Taenia solium. It is a loosely packed tissue that fills the spaces between the internal organs and the integumentary musculature. It consists of branched cells that form a syncytial network with fluid-filled interspaces. The mesenchyme does not contain a body cavity or a blood vascular system. It serves as a packing material that helps to maintain the shape and turgidity of the body and also acts as a hydraulic skeleton. It also facilitates the transport of substances to and from the tissues in the absence of a circulatory system.

The mesenchyme contains numerous round or oval calcareous bodies that are composed of concentric layers of calcium carbonate. These bodies are secreted by special mesenchymal cells called lime cells. The function of these calcareous bodies is not clear, but they may help to neutralize the acidic environment of the host`s intestine or act as a storage site for calcium ions.

The mesenchyme also contains some free cells that differentiate into reproductive organs in the mature proglottids. The mesenchyme is thicker in the young proglottids and the neck region than in the older proglottids.

The mesenchyme is divided into two zones by circular muscle fibers at the margins: an outer cortex or cortical zone and an inner medulla or medullary zone. The cortex contains more calcareous bodies and free cells than the medulla. The medulla contains more excretory vessels and nerve cords than the cortex.

Some possible ways to end the point are:

Therefore, the mesenchyme or parenchyma is an important component of the body wall of Taenia solium that provides structural support, protection, and transport functions.
In summary, the mesenchyme or parenchyma is a loose tissue layer that fills the body cavity of Taenia solium and performs various roles such as shape maintenance, calcium storage, and reproductive organ development.
Thus, the mesenchyme or parenchyma is a versatile tissue that adapts to the needs of Taenia solium by forming calcareous bodies, reproductive organs, and connecting with other tissues.